The invention relates to a process for improving color and color stability of oleic acid.
1. Background of the Invention
Oleic acid has many industrial and commercial uses and applications in which color is a major consideration. When oleic acid is introduced into many consumer products, a colorless or light colored material is required. In addition, when oleic acid is utilized in chemical processes as a reactant, color stability can be important if colorless or light colored products are required.
2. Related Art
It is known that the color and color stability of oleic acid is influenced by small amounts of minor components in oleic acid. The minor components and the effect on color and color stability are discussed in a series of articles which appeared in JAOCS, Vol. 59, No. 1 (January 1982) pgs.42-51; Sherman S. Lin et al., CHARACTERIZATION OF MINOR CONSTITUENTS IN COMMERCIAL OLEIC ACID, JOACS, Vol. 59, No. 1 (January 1982) pgs. 42-46; Yokunobo Murase et al., ORIGIN OF MINOR CONSTITUENTS OF COMMERCIAL OLEIC ACID; JAOCS, Vol. 59, No. 1 (January 1982) Pgs. 47-50; and Sherman S. Lin et al. qualitative and quantitative COMPARISON OF MINOR CONSTITUENTS IN DIFFERENT COMMERCIAL OLEIC ACIDS. JAOCS, Vol. 59, No. 1 (January 1982) Pgs. 50-51.
The articles disclose that about 1.2% of impurities in commercial oleic acid are responsible for the color and color instability of oleic acid. A portion of the color causing materials are present in the tallow (raw material) from which the oleic acid is produced and a portion of the color causing materials are formed during the production of oleic acid from tallow.
The articles disclose that the color causing materials (minor constituents) can be removed from oleic acid by adsorption on activated silicic acid. The method effectively removes the minor components from oleic acid. However, the adsorption method is generally not suitable for a commercial process due to the difficulty in regenerating the activated silicic acid or disposal of the spent solid.
Commercially, high purity, color stable oleic acid is produced by a combination of distillation and absorption methods with the consequent difficulty associated with handling and disposal of the solid adsorbent material. It would be useful to provide a commercial process which effectively improved the color and color stability of oleic acid without need for an absorption step. A number of distillation processes for fatty acids are disclosed in Diechelmann, G and Heinz, H. J., THE BASICS OF INDUSTRIAL OLEOCHEMISTRY, Peter Pomp GmbH (ISBN 3-89355-008-9), pages 52-74.
The color and color stability of oleic acid can be improved by a distillation process which comprises introducing an oleic acid feed into a first distillation zone having an enriching section and a stripping section to separate a minor amount of a topping product and a major amount of a bottoms product containing the oleic acid and introducing the bottoms produced containing oleic acid into a lower portion of a second distillation zone having an enriching section and removing the purified oleic acid as the top product and a residue fraction from the bottom of the second distillation zone.
The process effectively reduces the amounts of the minor components which are responsible for color formation and color instability and produces a commercially useful, color stable oleic acid without need for an adsorption step. The oleic acid produced by the process of the present invention can be superior to, or at least equivalent to, commercially available oleic acid produced by a distillation and adsorption method without the concomitant difficulties associated with handling and disposal of solid materials.